Special counsel Robert S. Mueller III submitted a long-awaited report to Attorney General William P. Barr on Friday, marking the end of his investigation into Russian interference in the 2016 election and possible obstruction of justice by President Trump.

The submission of Mueller’s report ends his closely watched inquiry — a case that has engulfed the Trump administration since its inception, leading to criminal charges against 34 people, including six former Trump associates and advisers.

A senior Justice Department official said the special counsel has not recommended any further indictments — a revelation that buoyed Trump’s supporters, even as other Trump-related investigations continue in other parts of the Justice Department. It is also unclear whether a Mueller report that does not result in additional charges could still hurt the president politically.

Justice Department officials notified Congress late Friday that they had received Mueller’s report, but they did not describe its contents. Barr is expected to summarize the findings for lawmakers as early as this weekend.

Only a small number of people inside the Justice Department know the document’s contents, but it immediately sparked a furious political reaction, with Democrats vying for the presidential nomination in 2020 demanding a public release of the findings and the two top Democrats in Congress, House Speaker Nancy Pelosi (D-Calif.) and Senate Minority Leader Charles E. Schumer (D-N.Y.), calling for the full report and its “underlying documentation” to be provided to Congress.

Trump’s supporters viewed the news as an optimistic indication that he was on the cusp of being vindicated.

“The fact that there are no more indictments is a big deal,” said David Bossie, a Trump ally. “This president has had his entire two-year presidency under a cloud of this fake, made-up Russian collusion story.”

Trump flew to his Florida resort Friday, accompanied by senior aides and White House lawyers. Trump did not immediately speak or tweet about the report’s delivery. Privately, some Trump advisers expressed relief that the report had been filed, but the president’s spokeswoman and lawyers were more guarded in their initial reaction.

White House press secretary Sarah Sanders said that the next steps “are up to Attorney General Barr, and we look forward to the process taking its course. The White House has not received or been briefed on the special counsel’s report.”

In a letter to the leaders of the House and Senate judiciary committees, Barr wrote that Mueller “has concluded his investigation of Russian interference in the 2016 election and related matters.”

Barr wrote that Mueller submitted a report to him explaining his prosecution decisions. The attorney general told lawmakers he was reviewing the report and anticipated that “I may be in a position to advise you of the Special Counsel’s principal conclusions as soon as this weekend.”

The attorney general wrote he would consult with Mueller and Deputy Attorney General Rod J. Rosenstein “to determine what other information from the report can be released to Congress and the public consistent with the law, including the Special Counsel regulations, and the Department’s long-standing practices and policies.”

Barr said there were no instances in the course of the investigation in which any of Mueller’s decisions were vetoed by his superiors at the Justice Department.

“I remain committed to as much transparency as possible, and I will keep you informed as to the status of my review,” Barr wrote.

After a week of growing expectation that Mueller’s report would soon arrive, a security officer from Mueller’s office delivered it Friday afternoon to Rosenstein’s office at Justice Department headquarters, according to spokeswoman Kerri Kupec. Within minutes of that delivery, the report was transmitted upstairs to Barr.

Around 4:35 p.m., White House lawyer Emmet Flood was notified that the Justice Department had received the report. Around that same time, Rosenstein called Mueller to personally thank him for his work, according to a Justice Department official.

About a half-hour after the White House was notified, a department official delivered Barr’s letter to the relevant House and Senate committees and senior congressional leaders, officials said.

One official described the report as “comprehensive” but added that very few people have seen it.

Even with the report’s filing, Mueller is expected to retain his role as special counsel for a wind-down period, though it is unclear how long that may last, officials said. A small number of his staffers will remain in the office to help shut down the operations.

“The investigation is complete,” Kupec said.

Two of the president’s attorneys, Rudolph W. Giuliani and Jay Sekulow, said in a joint statement: “We’re pleased that the Office of Special Counsel has delivered its report to the Attorney General pursuant to the regulations. Attorney General Barr will determine the appropriate next steps.”

Giuliani said he did not know whether he would get a briefing this weekend on the report’s contents.

Well before its completion, Mueller’s report was a hotly debated topic. Lawmakers sought to wrest guarantees from the Justice Department that the special counsel would give a complete public accounting of what he found during the nearly two-year inquiry.

According to Justice Department regulations, the special counsel’s report should explain Mueller’s decisions — who was charged, who was investigated but not charged, and why.

Mueller’s work consumed Washington and at times the country as the special counsel and his team investigated whether any Trump associates conspired with Russian officials to interfere in the election.

It is unclear how much of what Mueller found will be disclosed in Barr’s summary for Congress. Congressional Democrats, anticipating an incomplete accounting, have already sent extensive requests to the Justice Department for documents that would spell out what Mueller discovered.

Five people close to the president have pleaded guilty:Trump’s former campaign chairman, Paul Manafort; former deputy campaign manager Rick Gates; former national security adviser Michael Flynn; former personal attorney Michael Cohen; and former campaign adviser George Papadopoulos.

A sixth, Trump’s longtime friend Roger Stone, was indicted in January and accused of lying to Congress. He has pleaded not guilty.

More than two dozen of the people charged by Mueller are Russians, and because the United States does not have an extradition treaty with Russia, they are unlikely ever to see the inside of a U.S. courtroom.

None of the Americans charged by Mueller are accused of conspiring with Russia to interfere in the election — the central question of Mueller’s work. Instead, they pleaded guilty to various crimes, including lying to the FBI.

The investigation ended without charges for a number of key figures who had long been under Mueller’s scrutiny, including conservative writer Jerome Corsi, who said Friday that he felt “vindicated” by the development.

Corsi met with prosecutors repeatedly about communications he had before the November 2016 election with Stone about the anti-secrecy group WikiLeaks. In November, Corsi took the unorthodox step of publishing draft court documents Mueller’s team had provided to him as they urged him to plead guilty to lying in an October 2018 debriefing. He said that his memory had been faulty but that he had not intentionally lied, and he refused to take the deal.

“They lost. They tried to give me a plea deal that was a lie and I exposed it,” he said. “They wisely left me alone. Seven months through absolute hell when all I did was try to cooperate.”

The special counsel’s investigation was launched May 17, 2017, in a moment of crisis for the FBI, the Justice Department and the country.

Days earlier, Trump had fired FBI Director James B. Comey. The purported reason was Comey’s handling of the 2016 investigation of former secretary of state Hillary Clinton, but Trump said in an interview with NBC News shortly after the firing that he was thinking about the Russia inquiry when he decided to remove Comey.

Comey’s firing set off alarms in the Justice Department and in Congress, where lawmakers feared the president was determined to end the Russia investigation before it was completed.

After then-Attorney General Jeff Sessions recused himself from the Russia investigation, Rosenstein chose Mueller as special counsel in part to quell the burgeoning political crisis.

Mueller’s team pursued a number of investigative tracks, including whether the president’s behavior leading up to and after Comey’s firing amounted to an attempt to obstruct justice.

As the investigation proceeded, Republican opposition to Mueller’s work grew, encouraged in part by the president’s repeated declarations that the investigation was a “witch hunt.”

While those fights raged on, Mueller said virtually nothing. In part because of this silence, political factions tended to say almost anything they wanted about his work. Republicans in the House Freedom Caucus called it a money-wasting farce; Democrats touted every new investigative step as further evidence that the probe was so serious that Trump’s days as president could be numbered.

In 2018, Mueller’s office took direct aim at Moscow. Thirteen Russians were charged as part of an online “troll farm” accused of sowing political division and distrust among Americans via social media. Five months later, Mueller’s office indicted a dozen Russian military intelligence officials, saying they conspired to hack into Democrats’ computer accounts and publicize the stolen files.

Last year, much of Mueller’s time and energy was focused on the question of obstruction. Whether Trump or his senior advisers had sought to stop or cripple the Russia inquiry was a key reason that Mueller’s job as special counsel existed in the first place.

Proving a suspect’s intent is an important element of any obstruction case, and there was one witness Mueller was never able to get in a room: Trump. After negotiating for months, the president’s attorneys agreed to submit written answers to questions from the special counsel. Ultimately, Mueller and the Justice Department did not serve the president with a subpoena, which could have led to a fight at the Supreme Court.

Barr’s letter to Congress revealed Mueller’s superiors never rejected an investigative step he wanted to take — meaning Mueller never formally sought permission to subpoena the president.

Behind the scenes, however, Mueller and his team continued to hold the vague threat of a subpoena over Trump’s attorneys up until December, insisting they had to interview Trump to complete their work. Up until January, Mueller’s team had sought to have Trump answer additional questions.